Liquid crystal system and liquid crystal display

ABSTRACT

The instant invention relates to mesogenic systems comprising a) a polymeric component, component A, obtained or obtainable from polymerisation of a precursor comprising one or more mesogenic mono-reactive compounds, one or more di-reactive compounds, which optionally are also mesogenic compounds and optionally a photo-initiator and a low molecular weight component, component B, comprising one or more mono-reactive, mesogenic compounds, one or more mesogenic compounds and one or more chiral dopants, exhibiting a Blue Phase, as well as to the use of these systems in deices and to these devices.

FIELD OF THE INVENTION

The present invention relates to mesogenic media and to electro-opticaldisplays comprising these mesogenic media as light modulation media, inparticular to mesogenic media comprising polymeric material and todisplays, which are operated at a temperature at which the mesogenicmodulation media are in an optically isotropic phase, preferably in ablue phase.

PROBLEM TO BE SOLVED AND STATE OF THE ART

Electro-optical displays and mesogenic light modulation media, which arein the isotropic phase when being operated in the display are describedin DE 102 17 273 A. Electro-optical displays, and mesogenic lightmodulation media, which are in the so-called blue phase, when beingoperated in the display are described in DE 103 13 979.6.

The mesogenic media and displays described in these references provideseveral significant advantages compared to well-known and widely useddisplays using liquid crystals in the nematic phase, like for exampleliquid crystal displays (LCDs) operating in the twisted nematic (TN)-,the super twisted nematic (STN)-, the electrically controlledbirefringence (ECB)-mode with its various modifications like e.g. thevertically aligned nematic (VAN) mode and the in-plane switching(IPS)-mode. Amongst these advantages most pronounced are their muchfaster switching times, and significantly wider optical viewing angle.

Whereas, compared to displays using mesogenic media in another liquidcrystalline phase, as e.g. in the smectic phase in surface stabilizedferroelectric liquid crystal displays (SSF LCDs), the displays of DE 10217 273.0 and DE 103 13 979 are much easier to produce. For example, theydo not require a very thin cell gap and the electro-optical effect isnot very sensitive to small variations of the cell gap.

However, the liquid crystal media described in these mentioned patentapplications still require operating voltages, which are not low enoughfor some applications. Further the operating voltages of these mediavary with temperature, and it is generally observed, that at a certaintemperature the voltage dramatically increases with increasingtemperature. This limits the applicability of liquid crystal media inthe blue phase for display applications. A further disadvantage of theliquid crystal media described in these patent applications is theirmoderate reliability which is insufficient for very demandingapplications. This moderate reliability may be for example expressed interms of the voltage holding ratio parameter (VHR), which in liquidcrystal media as described above may be below 90%.

Some compounds and compositions have been reported which possess a bluephase between the cholesteric phase and the isotropic phase and canusually be observed by optical microscopy. These compounds orcompositions for which the blue phases are observed are typically singlemesogenic compounds or mixtures showing a high chirality. However,generally the blue phases observed only extend over a very smalltemperature range, which is typically less than 1 degree centigrade(Kelvin) wide. In order to operate the novel fast switching display modeof DE 103 13 979.6 the light modulation medium to be used has to be inthe blue phase. Thus a light modulation medium possessing a blue phase,which is as wide as possible, is required.

Therefore there is a strong need for a modulation medium with a bluephase with a wide phase range, which may be achieved either by anappropriate mixture of mesogenic compounds themselves or, preferably bymixing a host mixture with appropriate mesogenic properties with asingle dopant or a mixture of dopants that stabilises the blue phaseover a wide temperature range.

Kikuchi, H. et al., Polymeric Materials Science and Engineering (2002),1(1), 64-68 and Kikuchi, H. et al., Polymeric Materials Science andEngineering, (2003), 89, 90-91 describe in-situ polymerisation tostabilise the Blue Phase over a temperature range, which is 60° wide andincluding ambient temperature (206 to 326K), respectively over atemperature range, which is 120° wide and including room temperature(200K-326K) using a non-mesogenic mono-reactive monomer, such as 2-ethylhexyl acrylate together with a di-reactive mesogen (e.g. RM257,available from Merck KGaA) in a nematic host mixture.

H. Kikuchi, JP(A)2003-327966, describes a composite liquid crystal foruse as optical modulation element with specific composition comprising alow molecular weight liquid crystal, which possesses a Blue Phase and apolymer network within this medium obtained by polymerisation ofnon-liquid crystalline monomers together with a cross-linking agentRM257. In particular, the preferred embodiment is for branchedmonoacrylate monomers with alkyl side group as a side-chain.

However, these systems have significant drawbacks, as the precursors ofthe polymers are not particularly well soluble in the liquid crystalhosts, respectively in the mesogenic hosts, required for application indevices and/or as, in most cases, it is necessary to adjust thetemperature of the system during the process of polymerising theprecursor of the polymer, as the transition temperatures of themesophases and thus the temperature range over which the blue phaseexists, change during the very process.

Summarizing, there is a need for liquid crystal media, which can beoperated in liquid crystal displays, which are operated at temperatureswhere the media is in the blue phase, which provide the followingtechnical improvements:

-   -   a broad phase range of the blue phase,    -   a broad range of temperatures over which the electro-optical        effect can be used without the response time becoming too large        for practical applications,    -   ease of fabrication by good solubility of the precursors of the        polymer in the host and/or relative small change of the        transition temperatures during the process of the polymerisation        of the precursor of the polymer.    -   reduced operating voltage,    -   a reduced temperature dependency of the operating voltage and    -   an improved reliability, e.g. VHR.

PRESENT INVENTION

Surprisingly, it has now been found that mesogenic modulation mediacomprising a polymer obtainable from a precursor comprising amono-reactive mesogenic monomer, are suitable to considerably enhancethe range of temperatures over which the blue phase is stable or eveninduce a blue phase in respective mesogenic hosts, which do not showsuch a phase on their own. Preferably the mesogenic hosts are liquidcrystalline hosts.

Thus the present invention preferably relates to mesogenic systemscomprising:

-   -   a) a polymeric component, component A, obtained or obtainable        from polymerisation of a precursor comprising        -   i. one or more mesogenic mono-reactive compounds,        -   ii. one or more di-reactive compounds, which optionally are            also mesogenic compounds and        -   iii. optionally a photo-initiator and    -   b) a low molecular weight component, component B, comprising        -   iv. one or more mesogenic compounds and        -   v. one or more chiral dopants,    -   exhibiting a Blue Phase.

Preferably the system according to the present invention

-   -   comprise a component A comprising one or more mesogenic        di-reactive compounds and/or    -   comprise a component A comprising one or more non-mesogenic        (isotropic) mono-reactive compounds and/or    -   one or more compounds, which on their own lead or would lead to        an increase of the characteristic temperatures (e.g. the        transition temperature from the Blue Phase into the isotropic        phase) during and/or upon it's polymerisation and simultaneously        one or more compounds which on their own lead or would lead to a        decrease of the characteristic temperatures (e.g. the transition        temperature from the Blue Phase into the isotropic phase) during        and/or upon its polymerisation and/or    -   Exhibit characteristic temperatures, which do not change        significantly during and/or upon polymerisation of the precursor        of the polymer and/or    -   have a Blue Phase extending at least over a temperature range        from −10° C. or below to +50° C. or above.

The present invention further relates to light modulation elementscomprising one or more systems according to the present inventionelectro-optical displays comprising these light modulation elements.

The present invention also relates to the use of systems according tothe present invention as a light modulation media, as well as to the useof systems according to the present invention in light modulationelements.

In a further aspect the present invention relates to a process ofproducing a system according to the present invention, characterised inthat the characteristic temperature(s) of the system do not changesignificantly during the polymerisation of the precursor of the polymer.By this feature it is not necessary to adjust the temperature at whichthe polymerisation is performed during the process in order to keep itwithin the range of the blue phase, which is often required.

The mesogenic mono-reactive compounds used according to the presentinvention preferably comprise one or more ring elements, linked togetherby a direct bond or via a linking group and, where two of these ringelements optionally may be linked to each other, either directly or viaa linking group, which may be identical to or different from the linkinggroup mentioned. The ring elements are preferably selected from thegroup of four-, five-, six- or seven-, preferably of five- or six-,membered rings.

Preferably used are mono-reactive mesogens of formula IA

wherein

-   R¹¹ is H, F, Cl, Br, I, CN, NO₂, NCS, SF₅, SO₂CF₃ or alkyl which is    straight chain or branched, preferably has 1 to 20 C-atoms, is    unsubstituted, mono- or poly-substituted by F, Cl, Br, I or CN, and    in which one or more non-adjacent CH₂ groups are optionally    replaced, in each case independently from one another, by —O—, —S—,    —NH—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—-O—, —S—CO—,    —CO—S—, —CY¹═CY²— or —C≡C— in such a manner that O and/or S atoms    are not linked directly to one another, preferably H, Halogen,    n-alkyl, n-alkoxy with 1 to 7 C-atoms preferably 2 to 5 C-atoms,    alkenyl, alkenyloxy or alkoxyalkyl with 2 to 7 C-atoms, preferably    with 2 to 5 C-atoms or CN, NCS, halogen, preferably F, Cl,    halogenated alkyl, alkenyl or alkoxy, preferably mono-, di- or    oligo-fluorinated alkyl, alkenyl or alkoxy, especially preferred    CF₃, OCF₂H or OCF₃,-   R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to    12 C-atoms,

-    is a mesogenic moiety, preferably comprising one or more rings and    most preferably is a divalent radical of the formula

-    are, independently of each other, an aromatic and/or alicyclic    ring, or a group comprising two or more fused aromatic or alicyclic    rings, wherein these rings optionally contain one or more hetero    atoms selected from N, O and/or S, and are optionally mono- or    polysubstituted by R,-   Z¹¹ to Z¹⁴ are, independently of each other, —O—, —S—, —CO—, —CO—O—,    —O—CO—, —S—CO—, —CO—S—, —O—CO—O—, —CO—NR⁰¹—, —NR⁰¹—CO—, —OCH₂—,    —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF—, —CH₂CH₂—,    —CF₂CH₂—, —CH₂CF₂—, —CF₂CF₂—, —CH═N—, —N═CH—, —N═N—, —CH═CR⁰¹—,    —CY⁰¹═cy⁰²—, —C≡C—, —(CH₂)₄—, —CH═CH—CO—O—, —O—CO—CH═CH— or a single    bond,-   Y⁰¹ and Y⁰² are, independently of each other, F, CL or CN, and    alternatively one of them may be H,-   R is H or alkyl, preferably H or alkyl with 1 to 10 C-atoms,-   PG¹¹ is a polymerisable or reactive group,-   SG¹¹ is a spacer group or a single bond, and-   X¹¹ has one of the meanings given for Z¹¹ and preferably is —O—,    —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂— or a single bond.

In a preferred embodiment of the present invention the precursor of thepolymer comprises, besides the compound(s) of formula IA one or moredi-reactive mesogenic monomers, preferably of formula IB

wherein

has the meaning given for

under formula I above,

-   PG¹² and PG¹³, independently of each other, have one of the meanings    given for PG¹¹ under formula I above,-   SG¹² and SG¹³, independently of each other, have one of the meanings    given for SG¹¹ under formula I above, and-   X¹² and X¹³, independently of each other, have one of the meanings    given for X¹¹ under formula I above.

In a preferred embodiment the compounds according to the presentinvention are chiral compounds, i.e. a group with a chiral centre,preferably a chirally substituted atom and most preferably a chirallysubstituted C-atom.

Particularly preferred are polymer precursors comprising one or morecompounds of formula I and/or of formula II, wherein

-   -   Z¹¹ and/or Z¹⁴ is —O—, —CO—O—, —OCO—, —O—CO—O—, —CH₂—O—,        —O—CH₂—, —CF₂—O—, —O—CF₂—, —C≡C—, —CH═CH— or a single bond, most        preferably —CO—O— or —O—CO— or —O— and/or

-   Z¹¹ is different from a single bond and/or

-   ring A¹¹ is phenylene that is optionally substituted by one or more    groups R and/or

-   R¹¹ is alkyl or alkoxy with 1 to 12, preferably 1 to 8 C-atoms, or    alkenyl, alkenyloxy or alkynyl with 2 to 12, preferably 2 to 7    C-atoms and/or

-   SG¹¹ is alkylene with 1 to 12 C atoms which is optionally mono- or    polysubstituted by F and wherein one or more non-adjacent CH₂ may be    replaced, in each case independently from one another, by —O—,    —CH═CH— or —C≡C—, and that is linked to a ring, preferably to ring    A¹ via a group selected from —O—, —CO—O—, —O—CO—, —O—CO—O— and a    single bond and/or

-   SG¹¹ is a single bond.

Preferences for MG¹² to X¹³ are the same as for MG¹²X¹¹.

In a preferred embodiment rings A¹¹ to A¹³ are, independently of eachother, an aromatic or alicyclic ring, preferably a 5-, 6- or 7-memberedring, or a group comprising two or more, preferably two or three, fusedaromatic or alicyclic rings, wherein these rings optionally contain oneor more hetero atoms selected from N, O and/or S, and are optionallymono- or polysubstituted with L, wherein L is F, Cl, Br, CN, OH, NO₂,and/or an alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to12 C atoms, wherein one or more H atoms are optionally replaced by F orCl.

L is preferably F, Cl, CN, OH, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅, COCH₃,COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂ or OC₂F₅, in particular F, Cl,CN, CH₃, C₂H₅, OCH₃, COCH₃ or OCF₃, most preferably F, Cl, CH₃, OCH₃ orCOCH₃.

Preferred rings A¹¹ to A¹³ are, for example, furan, pyrrol, thiophene,oxazole, thiazole, thiadiazole, imidazole, phenylene, cyclohexylene,cyclohexenylene, pyridine, pyrimidine, pyrazine, azulene, indane,naphthalene, tetrahydronaphthalene, decahydronaphthalene,tetrahydropyrane, anthracene, phenanthrene and fluorene.

Particularly preferably one or more of these rings A¹¹ to A¹³ isselected from furane-2,5-diyl, thiophene-2,5-diyl,thienothiophene-2,5-diyl, dithienothiophene-2,6-diyl, pyrrol-2,5-diyl,1,4-phenylene, azulene-2,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl,naphthalene-2,6-diyl, 1,2,3,4-tetrahydro-naphthalene-2,6-diyl,indane-2,5-diyl, or 1,4-cyclohexylene wherein one or two non-adjacentCH₂ groups are optionally replaced by O and/or S, wherein these groupsare unsubstituted, mono- or polysubstituted by L as defined above.

Preferably

independently of each other, are,

or their mirror imageswherein

-   R is alkyl with 1 to 12 C-atoms, preferably with 1 to 7 C-atoms, or    alkenyl or alkynyl with 2 to 12 C-atoms, preferably with 2 to 7    C-atoms, in both of which one or more non-adjacent —CH₂— groups, not    adjacent to the phenyl ring, may be replaced by —O— and/or —CH═CH—    and/or one or more H-atoms may be replaced by halogen, preferably by    F,-    or their mirror images.    wherein-   R and R′, independently of one another, have one of the meanings    given for R above and preferably is alkyl, preferably methyl, ethyl    or propyl    and/or preferably

In a preferred embodiment of the present invention the group

contains only monocyclic rings A¹¹ to A¹³. Very preferably this is agroup with one or two 5- and/or 6-membered rings.

Preferred sub formulae for this group are listed below. For reasons ofsimplicity, Phe in these groups is 1,4-phenylene, PheL is a1,4-phenylene group which is substituted by 1 to 4 groups L as definedabove, Cyc is 1,4-cyclohexylene, Pyd is pyridine-2,5-diyl and Pyr ispyrimidine-2,5-diyl. The following list of preferred groups iscomprising the sub formulae I-1 to I-20 as well as their mirror images,

-Phe- I-1 -Pyd- I-2 —Pyr— I-3 -PheL- I-4 -Cyc- I-5 -Phe-Z-Cyc- I-6-Cyc-Z-Cyc- I-7 -PheL-Cyc- I-8 -Phe-Z-Phe- I-9 -Phe-Z-Pyd- I-10-Pyd-Z-Phe- I-11 -Phe-Z-Pyr— I-12 —Pyr-Z-Phe- I-13 -PheL-Z-Phe- I-14-PheL-Z-Pyd- I-15 -PheL-Z-Pyr— I-16 —Pyr-Z-Pyd- I-17 -Pyd-Z-Pyd- I-18—Pyr-Z-Pyr— I-19 -PheL-Z-PheL- I-20

In these preferred groups Z has the meaning of Z¹¹ as given in formulaI. Preferably Z is —COO—, —OCO—, —CH₂CH₂—, —C≡C— or a single bond.

Very preferably the group

is selected from the following formulae Ia to Ij and their mirror images

wherein L is F, Cl, Br, CN, OH, NO₂, and/or an alkyl, alkoxy,alkylcarbonyl or alkoxycarbonyl group with 1 to 12 C atoms, wherein oneor more H atoms are optionally replaced by F or Cl and r is 0, 1, 2, 3or 4, preferably 0, 1 or 2.

in these preferred formulae is very preferably

furthermore

with L having each independently one of the meanings given above.

Especially preferred compounds of formula I comprise at least one group

wherein r is 1 or 2

Further preferred compounds of formula I comprise at least two groups

wherein r is 1 and/or at least one group

wherein r is 2.

preferably is

wherein the 1,4-phenylene rings may optionally be sub-stituted by R,preferably by alkyl, preferably by methyl, and/or by alkoxy and/or byhalogen, preferably F.

More preferably

or their mirror imageswherein R has the meaning given above and preferably is alkyl,preferably with 1 to 6 C-atoms, preferably n-alkyl, wherein one or morenon-adjacent —CH₂-groups optionally may be replaced by —O— and/or by—CH═CH— and/or one or more H-atoms may be replaced by halogen,preferably by F.

An alkyl or an alkoxy radical, i.e. an alkyl where the terminal CH₂group is replaced by —O—, in this application may be straight-chain orbranched. It is preferably straight-chain, has 1, 2, 3, 4, 5, 6, 7 or 8carbon atoms and accordingly is preferably methyl, ethyl, propyl, butyl,pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy,heptoxy, or octoxy, furthermore methyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy,tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. an alkyl group in which one non-terminal CH₂ group isreplaced by —O—, is preferably straight-chain 2-oxapropyl(=methoxy-methyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl),2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for example.

An alkenyl group, i.e. an alkyl group wherein one or more CH₂ groups arereplaced by —CH═CH—, may be straight-chain or branched. It is preferablystraight-chain, has 2 to 10 C atoms and accordingly is preferably vinyl,prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- orpent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5-or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-,3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- ordec-9-enyl.

Especially preferred alkenyl groups are C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, inparticular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples for particularly preferred alkenyl groups are vinyl,1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl,3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl,4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groupshaving up to 5 C atoms are generally preferred.

In an alkyl group, wherein one CH₂ group is replaced by —O— and one by—CO—, these radicals are preferably neighboured. Accordingly theseradicals together form a carbonyloxy group —CO—O— or an oxycarbonylgroup —O—CO—. Preferably such an alkyl group is straight-chain and has 2to 6 C atoms.

It is accordingly preferably acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxy-ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxy-carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxy-carbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl, 4-(methoxycarbonyl)-butyl.

An alkyl group wherein two or more CH₂ groups are replaced by —O— and/or—COO—, it can be straight-chain or branched. It is preferablystraight-chain and has 3 to 12 C atoms. Accordingly it is preferablybis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl,4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxy-hexyl,7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl,10,10-bis-carboxy-decyl, bis-(methoxycarbonyl)-methyl,2,2-bis-(methoxycarbonyl)-ethyl, 3,3-bis-(methoxycarbonyl)-propyl,4,4-bis-(methoxycarbonyl)-butyl, 5,5-bis-(methoxycarbonyl)-pentyl,6,6-bis-(methoxycarbonyl)-hexyl, 7,7-bis-(methoxycarbonyl)-heptyl,8,8-bis-(methoxycarbonyl)-octyl, bis-(ethoxycarbonyl)-methyl,2,2-bis-(ethoxycarbonyl)-ethyl, 3,3-bis-(ethoxycarbonyl)-propyl,4,4-bis-(ethoxycarbonyl)-butyl, 5,5-bis-(ethoxycarbonyl)-hexyl.

A alkyl or alkenyl group that is monosubstituted by CN or CF₃ ispreferably straight-chain. The substitution by CN or CF₃ can be in anydesired position.

An alkyl or alkenyl group that is at least monosubstituted by halogen,it is preferably straight-chain. Halogen is preferably F or Cl, in caseof multiple substitution preferably F. The resulting groups include alsoperfluorinated groups. In case of monosubstitution the F or Clsubstituent can be in any desired position, but is preferably inω-position. Examples for especially preferred straight-chain groups witha terminal F substituent are fluormethyl, 2-fluorethyl, 3-fluorpropyl,4-fluorbutyl, 5-fluorpentyl, 6-fluorhexyl and 7-fluorheptyl. Otherpositions of F are, however, not excluded.

Halogen means F, Cl, Br and I and is preferably F or Cl, most preferablyF.

Each of R¹¹ to R¹⁴ may be a polar or a non-polar group. In case of apolar group, it is preferably selected from CN, SF₅, halogen, OCH₃, SCN,COR⁵, COOR⁵ or a mono-oligo- or polyfluorinated alkyl or alkoxy groupwith 1 to 4 C atoms. R⁵ is optionally fluorinated alkyl with 1 to 4,preferably 1 to 3 C atoms. Especially preferred polar groups areselected of F, Cl, CN, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, CHF₂,CH₂F, OCF₃, OCHF₂, OCH₂F, C₂F₅ and OC₂F₅, in particular F, Cl, CN, CF₃,OCHF₂ and OCF₃. In case of a non-polar group, it is preferably alkylwith up to 15 C atoms or alkoxy with 2 to 15 C atoms.

Each of R¹¹ and R¹² may be an achiral or a chiral group. In case of achiral group it is preferably of formula I*:

wherein

-   Q¹ is an alkylene or alkylene-oxy group with 1 to 9 C atoms or a    single bond,-   Q² is an alkyl or alkoxy group with 1 to 10 C atoms which may be    unsubstituted, mono- or polysubstituted by F, Cl, Br or CN, it being    also possible for one or more non-adjacent CH₂ groups to be    replaced, in each case independently from one another, by —O—, —S—,    —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO— or —CO—S— in    such a manner that oxygen atoms are not linked directly to one    another,-   Q³ is F, Cl, Br, CN or an alkyl or alkoxy group as defined for Q²    but being different from Q².

In case Q¹ in formula I* is an alkylene-oxy group, the O atom ispreferably adjacent to the chiral C atom.

Preferred chiral groups of formula I* are 2-alkyl, 2-alkoxy,2-methylalkyl, 2-methylalkoxy, 2-fluoroalkyl, 2-fluoroalkoxy,2-(2-ethin)-alkyl, 2-(2-ethin)-alkoxy, 1,1,1-trifluoro-2-alkyl and1,1,1-trifluoro-2-alkoxy.

Particularly preferred chiral groups I* are 2-butyl (=1-methylpropyl),2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, in particular 2-methylbutyl, 2-methylbutoxy,2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy,2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl,2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy,6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl,2-methylbutyryloxy, 3-methylvaleroyloxy, 4-methylhexanoyloxy,2-chlorpropionyloxy, 2-chloro-3-methylbutyryloxy,2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy,2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy,1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1-butoxypropyl-2-oxy,2-fluorooctyloxy, 2-fluorodecyloxy, 1,1,1-trifluoro-2-octyloxy,1,1,1-trifluoro-2-octyl, 2-fluoromethyloctyloxy for example. Verypreferred are 2-hexyl, 2-octyl, 2-octyloxy, 1,1,1-trifluoro-2-hexyl,1,1,1-trifluoro-2-octyl and 1,1,1-trifluoro-2-octyloxy.

In addition, compounds containing an achiral branched alkyl group mayoccasionally be of importance, for example, due to a reduction in thetendency towards crystallization. Branched groups of this type generallydo not contain more than one chain branch. Preferred achiral branchedgroups are isopropyl, isobutyl (=methylpropyl), isopentyl(=3-methylbutyl), isopropoxy, 2-methyl-propoxy and 3-methylbutoxy.

The polymerisable or reactive group PG¹¹ is preferably selected from

CH₂═CW¹—COO—,

CH₂═CW²—(O)_(k1)—, CH₃—CH═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—,(CH₂═CH)₂CH—O—, (CH₂═CH—CH₂)₂N—, HO—CW²W³—, HS—CW²W³—, HW²N—,HO—CW²W³—NH—, CH₂═CW¹—CO—NH—, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—,Phe-CH═CH—, HOOC—, OCN—, and W⁴W⁵W⁶Si—, with W¹ being H, Cl, CN, phenylor alkyl with 1 to 5 C-atoms, in particular H, Cl or CH₃, W² and W³being independently of each other H or alkyl with 1 to 5 C-atoms, inparticular methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ being independentlyof each other Cl, oxaalkyl or oxacarbonylalkyl with 1 to 5 C-atoms, Phebeing 1,4-phenylene and k₁ and k₂ being independently of each other 0 or1.

Especially preferably PG¹¹ is a vinyl group, an acrylate group, amethacrylate group, an oxetane group or an epoxy group, especiallypreferably an acrylate or methacrylate group.

As for the spacer group SG¹¹ all groups can be used that are known forthis purpose to those skilled in the art. The spacer group SG¹¹ ispreferably of formula SG′-X, such that PG¹¹-SG¹¹- is PG¹¹-SG′-X—,wherein

-   SG′ is alkylene with up to 20 C atoms which may be unsubstituted,    mono- or poly-substituted by F, Cl, Br, I or CN, it being also    possible for one or more non-adjacent CH₂ groups to be replaced, in    each case independently from one another, by —O—, —S—, —NH—, —NR⁰¹—,    —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—O—, —S—, —CO—, —CO—S—, —CH═CH—    or —C≡C— in such a manner that O and/or S atoms are not linked    directly to one another,-   X is —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR⁰¹—, —NR⁰¹—CO—,    —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—,    —CF₂CH₂—, —CH₂CF₂—, —CF₂CF₂—, —CH═N—, —N═CH—, —N═N—, —CH═CR⁰¹—,    CY⁰¹—CY⁰², —C≡C—, —CH═CH—COC—, —OCO—, —CH═CH— or a single bond, and-   R⁰¹, R⁰², Y⁰¹ and Y⁰² have one of the respective meanings given    above.-   X is preferably —O—, —S—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—,    —OCF₂—, —CF₂S—, —SCF₂—, —CH₂CH₂—, —CF₂CH₂—, —CH₂CF₂—, —CF₂CF₂—,    —CH═N—, —N═CH—, —N═N—, —CH═CR⁰—, —CY⁰²═CY⁰²—, —C≡C— or a single    bond, in particular —O—, —S—, —C≡C—, —CY⁰¹═CY⁰²— or a single bond,    very preferably a group that is able to from a conjugated system,    such as —C≡C— or —CY⁰¹═CY⁰²—, or a single bond.

Typical groups SG′ are, for example, —(CH₂)_(p)—,—(CH₂CH₂O)_(q)—CH₂CH₂—, —CH₂CH₂—S—CH₂CH₂— or —CH₂CH₂—NH—CH₂CH₂— or—(SiR⁰R⁰⁰—O)_(p)—, with p being an integer from 2 to 12, q being aninteger from 1 to 3 and R⁰, R⁰⁰ and the other parameters having themeanings given above.

Preferred groups SG′ are ethylene, propylene, butylene, pentylene,hexylene, heptylene, octylene, nonylene, decylene, undecylene,dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene,ethylene-thioethylene, ethylene-N-methyl-iminoethylene,1-methylalkylene, ethenylene, propenylene and butenylene for example.

In another preferred embodiment SG′ is a chiral group of formula I*′:

wherein

-   Q¹ and Q³ have the meanings given in formula I*, and-   Q⁴ is an alkylene or alkylene-oxy group with 1 to 10 C atoms or a    single bond, being different from Q¹,    with Q¹ being linked to the polymerisable group PG.

Further preferred are compounds with one or two groups PG¹¹-SG¹¹-wherein SG¹¹ is a single bond.

In case of compounds with two groups PG¹¹-SG¹¹, each of the twopolymerisable groups PG and the two spacer groups SG can be identical ordifferent.

Comprising in this application means in the context of compositions thatthe entity referred to, e.g. the medium or the component, contains thecompound or compounds in question, preferably in a total concentrationof 10% or more and most preferably of 20% or more.

Predominantly consisting, in this context, means that the entityreferred to contains 80% or more, preferably 90% or more and mostpreferably 95% or more of the compound or compounds in question.

Entirely consisting, in this context, means that the entity referred tocontains 98% or more, preferably 99% or more and most preferably 100.0%of the compound or compounds in question.

The concentration of the compounds of formula IA according to thepresent application are contained in the media according to the presentapplication preferably is in the range from 0.5% or more to 30% or less,more preferably in the range from 1% or more to 20% or less and mostpreferably in the range from 5% or more to 12% or less.

The concentration of the compounds of formula IB according to thepresent application are contained in the media according to the presentapplication preferably is in the range from 0.5% or more to 30% or less,more preferably in the range from 1% or more to 20% or less and mostpreferably in the range from 5% or more to 12% or less.

Exemplary compounds of formula IA, which can be beneficially usedaccording to the present invention, are those of sub-formulae IA-1 toIA-7

These compounds as pure substances have the phase sequences detected byDSC which are given in the following table, table a.

TABLE a Phase sequences of mono-reactive mesogens Phase sequenceCompound No. T/° C. IA-1 K 81Ch 128 I IA-2 K 35 (S_(A)-8) I [Ch-1.2 I]IA-3 K 38.5 (^(N)*/_(SA)-3.2) I [N −1.14 I by DSC] IA-4 K 89.0 N* IA-5 K66 S_(X) 71 S 129 N 151 I IA-6 K 60.4 S_(A) 96.2 Ch 119.6 I IA-7 K 73.3S_(A) 102 N 151 I

Exemplary compounds of formula IB, which can be beneficially usedaccording to the present invention, are those of sub-formulae iB-1 toIB-7

These compounds as pure substances have the phase sequences detected byDSC, which are given in the following table, table b.

TABLE b Phase sequences of di-reactive mesogens Phase sequence CompoundNo. T/° C. IB-1 K 78 N 103 I IB-2 K 68 S_(A) 75 N 79 I IB-3 K 88 N 118 IIB-4 K 61 (N 48) I IB-5 K 83 I IB-6 K 66 N 127 I IB-7 K 78 N 103 I

The compounds of formulae IA-1 to IA-6 and IB-1 to IB-7 are easilyaccessible and available from Merck KGaA.

In a preferred embodiment the mesogenic modulation media according tothe instant invention comprise a polymeric material obtained orobtainable from a mixture of polymer precursors comprising

-   -   a component I comprising one or more mesogenic mono-reactive        monomers and/or    -   a component II comprising one or more mono-reactive mesogenic        monomers.

Preferably the mixture of polymer precursors has the same or almost thesame transition temperature or temperatures, in particular the sameclearing point and/or transition temperature from the cholesteric phaseto the blue phase (T(Ch,BP) also called T(N*,BP)) and/or transitiontemperature from the blue phase to the isotropic phase (T(BP,I)), orleads to no or only to a limited change of one or more of thesetemperatures during the process of its polymerisation.

Preferably the precursor of the polymer comprises

-   -   one or more mono-reactive mesogenic monomers having one or more        of the transition temperatures mentioned directly above, which        are above the respective values of the mesogenic host mixture,        component B of the systems, respectively leading to a decrease        of the respective temperature during the process of        polymerisation, and    -   having one or more of the said respective transition        temperatures, which are below the respective values of the        mesogenic host mixture, component B of the systems, respectively        leading to an increase of the respective temperature during the        process of polymerisation.

In a preferred embodiment the mono-reactive polymer precursors havingtransition temperatures, e.g. a clearing point below that of themesogenic host mixture, respectively leading to an increase of thetransiton temperatures during the process of polymerisation, arenonmesogenic compounds.

In another preferred embodiment of the present invention the polymerprecursor comprises

-   -   one mono-reactive mesogenic monomer, which having a clearing        point, which is identical are at least almost identical to that        of the mesogenic host mixture, respectively leading to no or        almost no decrease of the said respective transition temperature        or temperatures during the process of polymerisation.

Preferably the Blue Phase of the low molecular weight component,component B in the system with the polymerized polymer precursor extendsfrom 30° C. or less to 70° or more, more preferably from 20° C. or lessto 70° or more, more preferably from 0° C. or less to 80° or more andmost preferably from −20° C. or less to 80° or more.

In a preferred embodiment the mesogenic modulation media according tothe instant invention comprise

-   -   a component A, preferably in a concentration of 1% to 25% by        weight, comprising, preferably predominantly consisting of and        most preferably entirely consisting of, one compound or more        compounds of the formula I given above and    -   optionally a dielectrically positive component B comprising,        preferably predominantly consisting of and most preferably        entirely consisting of one compound or of more compounds of        formula II

wherein

-   R² has the meaning given under formula I for R¹¹,-   A²¹, A²² and A²³ are, each independently of each other,

-    whereby each of A²¹ and A²² may have the same or a different    meaning if present twice,-   Z²¹ and Z²² are, each independently of each other, a single bond,    —(CH₂)₄)—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—, —CH₂—CF₂—, —CH═CH—,    —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CF—, —C≡C—, —CH₂O—,    —OCH₂—, —CF₂O—, —OCF₂—, —CO—O— or —O—CO—, whereby each of Z²¹ and    Z²² may have the same or a different meaning if present twice,-   X² is halogen, —CN, —NCS, —SF₅, —SO₂CF₃, alkyl, alkenyl, alkenyloxy    or alkylalkoxy or alkoxy radical each mono- or polysubstituted by CN    and/or halogen,-   L²¹ and L²² are, each independently of each other, H or F, and-   m is 0, 1 or 2,-   n iso, 1, 2 or 3,-   o is 0, 1 or 2, preferably 0 or 1 and-   m+n+o is 3 or less, preferably 2 or less,    -   optionally a component C, preferably in a concentration of 1% to        25% by weight, comprising, preferably predominantly consisting        of and most preferably entirely consisting of one compound or of        more compounds of formula III

wherein

-   a, b, c and d are each independently of each other 0, 1 or 2,    whereby-   a+b+c+d is 4 or less,-   A³¹, A³², A³³-   and A³⁴ are, each independently of each other,

-    whereby each of A³¹, A³², A³³ and A³⁴ may have the same or a    different meaning if present twice,-   Z³¹, Z³², Z³³-   and Z³⁴ are, each independently of each other, a single bond,    —(CH₂)₄)—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—, —CH₂—CF₂—, —CH═CH—,    —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CF—, —C≡D—, —CH₂O—,    —OCH₂—, —CF₂O—, —OCF₂—, —CO—O— or —O—CO—, whereby each of Z³¹, Z³²,    Z³³ and Z³⁴ may have the same or a different meaning if present    twice,-   R³ is an alkyl or alkoxy radical having from 1 to 15 carbon atoms,    wherein one or more methylene groups of said alkyl or alkoxy radical    may be replaced independently of each other by —O—, —S—,    —SiR^(x)R^(y)—, —CH═CH—, —C≡D—, —CO—O— and/or —O—CO— such that    oxygen and/or sulfur atoms are not linked directly to each other,    said alkyl or alkoxy radical being unsubstituted or mono-substituted    with a —CN group or mono- or poly-substituted with halogen,    preferably R¹¹ is a straight-chain alkyl, alkoxy, alkenyl,    alkenyloxy or —O-alkylene-O-alkyl radical with up to 10 carbon    atoms, said radicals being unsubstituted or mono- or    poly-substituted with halogen,-   L³¹, L³², L³³-   and L³⁴ are each independently of each other hydrogen, halogen, a CN    group, an alkyl or alkoxy radical having from 1 to 15 carbon atoms    wherein one or more methylene groups of said alkyl or alkoxy radical    may be replaced independently of each other by —O—, —S—,    —SiR^(x)R^(y)—, —CH═CH—, —C≡D—, —CO—O— and/or —O—CO— such that    oxygen and/or sulfur atoms are not linked directly to each other,    said alkyl or alkoxy radical being unsubsti-tuted or    mono-substituted with a —CN group or mono- or poly-substituted with    halogen, with the proviso that at least one of L³¹, L³², L³³ and L³⁴    is not hydrogen,-   X³ is F, Cl, CF₃, OCF₃, CN, NCS, —SF₅ or —SO₂—R^(z),-   R^(x) and R^(y) are independently of each other hydrogen or an alkyl    radical having from 1 to 7 carbon atoms; preferably R^(x) and R^(y)    are both methyl, ethyl, propyl or butyl, and-   R^(z) is an alkyl radical having from 1 to 7 carbon atoms, said    alkyl radical being unsubstituted or mono- or poly-substituted with    halogen; preferably R^(z) is CF₃, C₂F₅ or n-C₄F₉ and    -   1-20% by weight of component D comprising one chiral compound or        more chiral compounds with a HTP of ≧20 μm.

The inventive mixtures contain 1-25 wt. %, preferably 2-20 wt. % andmost preferably 3-15 wt. % of component A.

Suitable chiral compounds of component D are those, which have anabsolute value of the helical twisting power of 20 μm or more,preferably of 40 μm or more and most preferably of 60 μm or more. TheHTP is measured in MLD-6260 at a temperature of 20° C.

The chiral component D comprises preferably one or more chiral compoundswhich have a mesogenic structure and exhibit preferably one or moremesophases themselves, particularly at least one cholesteric phase.Preferred chiral compounds being comprised in the chiral component Dare, inter alia, well known chiral dopants like cholesteryl-nonanoate(CN), R/S-811, R/S-1011, R/S-2011, R/S-3011, R/S-4011, R/S-5011, CB-15(Merck KGaA, Darmstadt, Germany). Preferred are chiral dopants havingone or more chiral moieties and one or more mesogenic groups or havingone or more aromatic or alicyclic moieties forming, together with thechiral moiety, a mesogenic group. More preferred are chiral moieties andmesogenic chiral compounds disclosed in DE 34 25 503, DE 35 34 777, DE35 34 778, DE 35 34 779, DE 35 34 780, DE 43 42 280, EP 01 038 941 andDE 195 41 820 that disclosure is incorporated within this application byway of reference. Particular preference is given to chiral binaphthylderivatives as disclosed in EP 01 111 954.2, chiral binaphtholderivatives as disclosed in WO 02/34739, chiral TADDOL derivatives asdisclosed in WO 02/06265 as well as chiral dopants having at least onefluorinated linker and one end chiral moiety or one central chiralmoiety as disclosed in WO 02/06196 and WO 02/06195.

The controlling medium of the present invention has a characteristictemperature, preferably a clearing point, in the range from about −30°C. to about 80° C., especially up to about 55° C.

The inventive mixtures contain one ore more (two, three, four or more)chiral compounds in the range of 1-25 wt. %, preferably 2-20 wt. %.

Especially preferred are mixtures containing 3-15 wt. % of a chiralcompound.

Preferred embodiments are indicated below:

-   -   The medium comprises one, two or more compounds of formula I;    -   Component B preferably contains besides one compound ore more        compounds of formula II one ester compound or more ester        compounds of the formula Z

-   -    wherein R^(Z) has the meaning given under formula I for R¹¹,

-   -    X^(Z) is F, Cl, CN, NCS, OCF₃, CF₃ or SF₅.    -    wherein R^(Z) has the meaning given under formula II for R².    -   Especially preferred are mixtures containing 5% to 35%,        preferably 10% to 30% and especially preferred 10% to 20% of        compounds of formula Z.    -   The component B preferably contains additionally one or more        compounds of formula N

-   -    wherein        -   R has the meaning given under formula I for R¹¹ and            preferably is alkyl or Alkyl-C≡C,        -   “Alkyl” is alkyl with 1 to 7 C-atoms, preferably n-alkyl,            and        -   n is 0 or 1.    -   The component B preferably additionally comprises one or more        compounds selected from the group of ester compounds of formulae        E

-   -    in which R⁰ has the meaning given for R¹¹ under formula I and        preferably is alkyl and

-   -   The proportion of the compounds of the formulae E is preferably        10-30% by weight, in particular 15% to 25%.    -   The medium preferably comprises one compound or more compounds        selected from the group of formulae Q-1 and Q-2

-   -    wherein R⁰ has the meaning given for R¹¹ under formula I and n        and m are, independently of each other 0 or 1.    -   The medium preferably comprises one compound or more compounds        selected from the group of compounds of formulae II in which R⁰        is methyl.    -   The medium preferably comprises one dioxane compound, two or        more dioxane compounds, preferably one dioxane compound or two        dioxane compounds, selected from the group of formulae Dx-1 and        Dx-2

-   -    wherein R⁰ has the meaning given for R¹¹ under formula I.

It has been found that even a relatively small proportion of compoundsof the formulae I mixed with conventional liquid-crystal materials, butin par-ticular with one or more compounds of the formulae II and III,results in a lower operating voltage and a broader operating temperaturerange. Preference is given, in particular, to mixtures which, besidesone or more compounds of the formula I, comprise one or more compoundsof the formula II, in particular compounds of the formula II in which X²is F, Cl, CN, NCS, CF₃ or OCF₃. The compounds of the formulae I to IIIare colourless, stable and readily miscible with one another and withother liquid-crystalline materials.

The optimum mixing ratio of the compounds of the formulae I and II andIII depends substantially on the desired properties, on the choice ofthe components of the formulae I, II and/or III, and on the choice ofany other components that may be present. Suitable mixing ratios withinthe range given above can easily be determined from case to case.

The total amount of compounds of the formulae I to III in the mixturesaccording to the invention is not crucial. The mixtures can thereforecomprise one or more further components for the purposes of optimisationof various properties. However, the observed effect on the operatingvoltage and the operating temperature range is generally greater, thehigher the total concentration of compounds of the formulae I to III.

In a particularly preferred embodiment, the media according to theinven-tion comprise compounds of the formula III which X³ is F, OCF₃,OCHF₂, OCH═CF₂, OCF═CF₂ or OCF₂—CF₂H. A favourable synergistic effectwith the compounds of the formulae I results in particularlyadvantageous prop-erties. In particular, mixtures comprising compoundsof formula I and of formula II and of formula III are distinguished bytheir low operating voltages.

The individual compounds of the formulae II to III and their respectivesub-formulae which can be used in the media according to the inventionare either known or can be prepared analogously to the known compounds.

The construction of the displays according to the invention frompolarisers, electrode base plates and surface-treated electrodescorresponds to the conventional construction for displays of this type.The term conventional construction is broadly drawn here and also coversall derivatives and modifications of the MLC display, in particularincluding matrix display elements based on poly-Si TFT or MIM, however,particularly preferred are displays, which have electrodes on just oneof the substrates, i.e. so called interdigital electrodes, as those usedin IPS displays, preferably in one of the established structures.

A significant difference between the displays according to the inventionand the conventional displays based on the twisted nematic cellconsists, however, in the choice of the liquid-crystal parameters of theliquid-crystal layer.

The media according to the invention are prepared in a mannerconven-tional per se. In general, the components are dissolved in oneanother, advantageously at elevated temperature. By means of suitableadditives, the liquid-crystalline phases in accordance with theinvention can be modified in such a way that they can be used in alltypes of liquid crystal display elements that have been disclosedhitherto. Additives of this type are known to the person skilled in theart and are described in detail in the literature (H. Kelker and R.Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). Forexample, pleochroic dyes can be added for the preparation of colouredguest-host systems or substances can be added in order to modify thedielectric anisotropy, the viscosity and/or the alignment of the nematicphases. Furthermore, stabilisers and antioxidants can be added.

The mixtures according to the invention are suitable for TN, STN, ECBand IPS applications and isotropic switching mode (ISM) applications.Hence, their use in an electro-optical device and an electro-opticaldevice containing liquid crystal media comprising at least one compoundaccording to the invention are subject matters of the present invention.

The inventive mixtures are highly suitable for devices which operate inan optically isotropic state. The mixtures of the invention aresurprisingly found to be highly suitable for the respective use.

Electro-optical devices that are operated or operable in an opticallyisotropic state recently have become of interest with respect to video,TV, and multi-media applications. This is because conventional liquidcrystal displays utilizing electro-optical effects based on the physicalproperties of liquid crystals exhibit a rather high switching time,which is undesired for said applications. Furthermore most of theconventional displays show a significant viewing angle dependence ofcontrast that in turn makes necessary measures to compensate thisundesired property.

With regard to devices utilizing electro-optical effects in an isotropicstate the German Patent Application DE 102 17 273 A1 for examplediscloses light controlling (light modulation) elements in which themesogenic controlling medium for modulation is in the isotropic phase atthe operating temperature. These light controlling elements have a veryshort switching time and a good viewing angle dependence of contrast.However, the driving or operating voltages of said elements are veryoften unsuitably high for some applications.

German Patent Application DE 102 41 301 yet unpublished describesspecific structures of electrodes allowing a significant reduction ofthe driving voltages. However, these electrodes make the process ofmanufacturing the light controlling elements more complicated.

Furthermore, the light controlling elements, for example, disclosed inboth DE 102 17 273 A1 and DE 102 41 301 show a significant temperaturedependence. The electro-optical effect that can be induced by theelectrical field in the controlling medium being in an optical isotropicstate is most pronounced at temperatures close to the clearing point ofthe controlling medium. In this range the light controlling elementshave the lowest values of their characteristic voltages and, thus,require the lowest operating voltages. As temperature increases thecharacteristic voltages and hence the operating voltages increaseremarkably. Typical values of the temperature dependence are in therange from about a few volts per centigrade up to about ten or morevolts per centigrade. While DE 102 41 301 describes various structuresof electrodes for devices operable or operated in the isotropic state,DE 102 17 273 A1 discloses isotropic media of varying composition thatare useful in light controlling elements operable or operated in theisotropic state. The relative temperature dependence of the thresholdvoltage in these light controlling elements is at a temperature of 1centigrade above the clearing point in the range of about50%/centigrade. That temperature dependence decreases with increasingtemperature so that it is at a temperature of 5 centigrade above theclearing point of about 10%/centigrade. However, for many practicalapplications of displays utilizing said light controlling elements thetemperature dependence of the electro-optical effect is too high. To thecontrary, for practical uses it is desired that the operating voltagesare independent from the operating temperature over a temperature rangeof at least some centigrades, preferably of about 5 centigrades or more,even more preferably of about 10 centigrades or more and especially ofabout 20 centigrades or more.

Now it has been found that the use of the inventive mixtures are highlysuitable as controlling media in the light controlling elements asdescribed above and in DE 102 17 273 A1, DE 102 41 301 and DE 102 536 06and broaden the temperature range in which the operating voltages ofsaid electro-optical operates. In this case the optical isotropic stateor the blue phase is almost completely or completely independent fromthe operating temperature.

This effect is even more distinct if the mesogenic controlling mediaexhibit at least one so-called “blue phase” as described in yetunpublished DE 103 13 979. Liquid crystals having an extremely highchiral twist may have one or more optically isotropic phases. If theyhave a respective cholesteric pitch, these phases might appear bluish ina cell having a sufficiently large cell gap. Those phases are thereforealso called “blue phases” (Gray and Goodby, “Smectic Liquid Crystals,Textures and Structures”, Leonhard Hill, USA, Canada (1984)). Effects ofelectrical fields on liquid crystals existing in a blue phase aredescribed for instance in H. S. Kitzerow, “The Effect of Electric Fieldson Blue Phases”, Mol. Cryst. Liq. Cryst. (1991), Vol. 202, p. 51-83, aswell as the three types of blue phases identified so far, namely BP I,BP II, and BP III, that may be observed in field-free liquid crystals.It is noteworthy, that if the liquid crystal exhibiting a blue phase orblue phases is subjected to an electrical field, further blue phases orother phases different from the blue phases I, II and III might appear.

The inventive mixtures can be used in an electro-optical lightcontrolling element, which comprises

-   -   one or more, especially two substrates;    -   an assembly of electrodes;    -   one or more elements for polarizing the light; and    -   said controlling medium;        whereby said light controlling element is operated (or operable)        at a temperature at which the controlling medium is in an        optically isotropic phase when it is in a non-driven state.

The operating temperature of the light controlling elements ispreferably above the transition temperature of the controlling medium tothe blue phase; generally the operating temperature is in the range ofabout 0.1° to about 50°, preferably in the range of about 0.1° to about40° above said temperature. It is highly preferred that the operatingtemperature is in the range from the transition temperature of thecontrolling medium to the blue phase up to the transition temperature ofthe controlling medium from the blue phase to the isotropic phase, whichis the clearing point. The light controlling elements, however, may alsobe operated at temperatures at which the controlling medium is in theisotropic phase.

For the purposes of the present invention the term “characteristictemperature” is defined as follows:

-   -   If the characteristic voltage as a function of temperature has a        minimum, the temperature at this minimum is denoted as        characteristic temperature.    -   If the characteristic voltage as a function of temperature has        no minimum and if the controlling medium has one or more blue        phases, the transition temperature to the blue phase is denoted        as characteristic temperature; in case there are more than one        blue phase, the lowest transition temperature to a blue phase is        denoted as characteristic temperature.    -   If the characteristic voltage as a function of temperature has        no minimum and if the controlling medium has no blue phase, the        transition temperature to the isotropic phase is denoted as        characteristic temperature.

In the context of the present invention the term “alkyl” means, as longas it is not defined in a different manner elsewhere in this descriptionor in the claims, straight-chain and branched hydrocarbon (aliphatic)radicals with 1 to 15 carbon atoms. The hydrocarbon radicals may beunsubstituted or substituted with one or more substituents beingindependently selected from the group consisting of F, Cl, Br, I or CN.

The dielectrics may also comprise further additives known to the personskilled in the art and described in the literature. For example, 0 to 5%of pleochroic dyes, antioxidants or stabilizers can be added. C denotesa crystalline phase, S a smectic phase, S_(C) a smectic C phase, N anematic phase, I the isotropic phase and BP the blue phase.

V_(X) denotes the voltage for X % transmission. Thus e.g. V₁₀ denotesthe voltage for 10% transmission and V₁₀₀ denotes the voltage for 100%transmission (viewing angle perpendicular to the plate surface). t_(on)(respectively τ_(on)) denotes the switch-on time and t_(off)(respectively τ_(off)) the switch-off time at an operating voltagecorresponding the value of V₁₀₀, respectively of V_(max).

Δn denotes the optical anisotropy. Δ∈ denotes the dielectric anisotropy(Δ∈=∈_(∥)−∈_(⊥), where ∈_(∥) denotes the dielectric constant parallel tothe longitudinal molecular axes and ∈_(⊥) denotes the dielectricconstant perpendicular thereto). The electro-optical data are measuredin a TN cell at the 1^(st) minimum of transmission (i.e. at a (d·Δn)value of 0.5 μm) at 20° C., unless expressly stated otherwise. Theoptical data are measured at 20° C., unless expressly stated otherwise.

Optionally, the light modulation media according to the presentinvention can comprise further liquid crystal compounds in order toadjust the physical properties. Such compounds are known to the expert.Their concentration in the media according to the instant invention ispreferably 0% to 30%, more preferably 0% to 20% and most preferably 5%to 15%.

Preferably the mesogenic media of the inventive systems have a range ofthe blue phase or, in case of the occurrence of more than one bluephase, a combined range of the blue phases, with a width of 9° or more,preferably of 10° or more, more preferably of 15° or more and mostpreferably of 20° or more.

In a preferred embodiment this phase range at least from 10° C. to 30°C., most preferably at least from 10° C. to 40° C. and most preferablyat least from 0° C. to 50° C., wherein at least means, that preferablythe phase extends to temperatures below the lower limit and at the sametime, that it extends to temperatures above the upper limit.

In another preferred embodiment this phase range at least from 20° C. to40° C., most preferably at least from 30° C. to 80° C. and mostpreferably at least from 30° C. to 90° C. This embodiment isparticularly suited for displays with a strong back light, dissipatingenergy and thus heating the display. Also preferred are systems with arange from at least −20° C. to 50° C.

In the present application the term dielectrically positive compoundsdescribes compounds with Δ∈>1.5, dielectrically neutral compounds arecompounds with −1.5≦Δ∈≦1.5 and dielectrically negative compounds arecompounds with Δ∈<−1.5. The same holds for components. Δ∈ is determinedat 1 kHz and 20° C. The dielectrical anisotropies of the compounds isdetermined from the results of a solution of 10% of the individualcompounds in a nematic host mixture. The capacities of these testmixtures are determined both in a cell with homeotropic and withhomogeneous alignment. The cell gap of both types of cells isapproximately 20 μm. The voltage applied is a rectangular wave with afrequency of 1 kHz and a root mean square value typically of 0.5 V to1.0 V, however, it is always selected to be below the capacitivethreshold of the respective test mixture.

For dielectrically positive compounds the mixture ZLI-4792 and fordielectrically neutral, as well as for dielectrically negativecompounds, the mixture ZLI-3086, both of Merck KGaA, Germany are used ashost mixture, respectively. The dielectric permittivities of thecompounds are determined from the change of the respective values of thehost mixture upon addition of the compounds of interest and areextrapolated to a concentration of the compounds of interest of 100%.

Components having a nematic phase at the measurement temperature of 20°C. are measured as such, all others are treated like compounds.

The term threshold voltage refers in the instant application to theoptical threshold and is given for 10% relative contrast (V₁₀) and theterm saturation voltage refers to the optical saturation and is givenfor 90% relative contrast (V₉₀) both, if not explicitly statedotherwise. The capacitive threshold voltage (V₀, also calledFreedericksz-threshold V_(Fr)) is only used if explicitly mentioned.

The ranges of parameters given in this application are all including thelimiting values, unless explicitly stated otherwise.

Throughout this application, unless explicitly stated otherwise, allconcentrations are given in mass percent and relate to the respectivecomplete mixture, all temperatures are given in degrees centigrade(Celsius) and all differences of temperatures in degrees centigrade. Allphysical properties have been and are determined according to “MerckLiquid Crystals, Physical Properties of Liquid Crystals”, StatusNovember 1997, Merck KGaA, Germany and are given for a temperature of20° C., unless explicitly stated otherwise. The optical anisotropy (Δn)is determined at a wavelength of 589.3 nm. The dielectric anisotropy(Δ∈) is determined at a frequency of 1 kHz. The threshold voltages, aswell as all other electro-optical properties have been determined withtest cells prepared at Merck KGaA, Germany. The test cells for thedetermination of Δ∈ had a cell gap of 22 μm. The electrode was acircular ITO electrode with an area of 1.13 cm² and a guard ring. Theorientation layers were lecithin for homeotropic orientation (∈_(∥)) andpolyimide AL-1054 from Japan Synthetic Rubber for homogenous orientation(∈_(⊥)). The capacities were determined with a frequency responseanalyser Solatron 1260 using a sine wave with a voltage of 0.3 or 0.1V_(rms). The light used in the electro-optical measurements was whitelight. The set up used was a commercially available equipment ofAutronic Melchers, Karlsruhe, germany: DMS 301 reespectively DMS 730.The characteristic voltages have been determined under perpendicularobservation. The threshold voltage (V₁₀), mid-grey voltage (V₅₀) andsaturation voltage (V₉₀) have been determined for 10%, 50% and 90%relative contrast, respectively.

The mesogenic modulation material has been filled into an electrooptical test cell prepared at the respective facility of Merck KGaA. Thetest cells had inter-digital electrodes on one substrate side. Theelectrode width was 10 μm, the distance between adjacent electrodes was10 μm and the cell gap was also 10 μm. This test cell has been evaluatedelectro-optically between crossed polarisers.

At low temperatures, the filled cells showed the typical texture of achiral nematic mixture, with an optical transmission between crossedpolarisers without applied voltage. Upon heating, at a first temperature(T₁) the mixtures turned optically isotropic, being dark between thecrossed polarisers. This indicated the transition from the chiralnematic phase to the blue phase at that temperature. Up to a secondtemperature (T₂) the cell showed an electro-optical effect under appliedvoltage, typically of some tens of volts, a certain voltage in thatrange leading to a maximum of the optical transmission. Typically at ahigher temperature the voltage needed for a visible electro-opticaleffect increased strongly, indicating the transition from the blue phaseto the isotropic phase at this second temperature (T₂).

The temperature range (ΔT(BP)), where the mixture can be usedelectro-optically in the blue phase most beneficially has beenidentified as ranging from T₁ to T₂. This temperature range (ΔT(BP)) isthe temperature range given in the examples of this application. Theelectro-optical displays can also be operated at temperatures beyondthis range, i.e. at temperatures above T₂, albeit only at significantlyincreased operation voltages.

At low temperatures the cell show the typical texture of a chiralnematic mixture, with an optical transmission between crossed polariserswithout applied voltage. On heating, at a the temperature T₁ the mixturebecomes optically isotropic, being dark between the crossed polarisers.This indicates the transition from the chiral nematic phase to the bluephase. Upon further hearting the cell showed a clear electro opticaleffect under applied voltage up to the temperature T₂.

The temperature range (ΔT(BP)), where the mixture can be usedelectro-optically in the blue phase is T₁ to T₂,

Besides the operation voltages also the response times, both forswitching on (Δ_(on)) and for switching off (Δ_(off)), do significantlydepend on the temperature. The response times decrease with increasingtemperature above T₁ and the temperature at which both response timeshave fallen below 5 ms each is called (T₃). The temperature range overwhich the cells can be utilized satisfying both conditions, i.e. arehaving a reasonably low opreation voltage and each of the two responsetimes being below 5 ms, is called usable flat range or short flat rangeand given as: ΔT(FR)=T₂−T₃.

The liquid crystal media according to the present invention can containfurther additives and chiral dopants in usual concentrations. The totalconcentration of these further constituents is in the range of 0% to10%, preferably 0.1% to 6%, based in the total mixture. Theconcentrations of the individual compounds used each are preferably inthe range of 0.1 to 3%. The concentration of these and of similaradditives is not taken into consideration for the values and ranges ofthe concentrations of the liquid crystal components and compounds of theliquid crystal media in this application.

The inventive liquid crystal media according to the present inventionconsist of several compounds, preferably of 3 to 30, more preferably of5 to 20 and most preferably of 6 to 14 compounds. These compounds aremixed in conventional way. As a rule, the required amount of thecompound used in the smaller amount is dissolved in the compound used inthe greater amount. In case the temperature is above the clearing pointof the compound used in the higher concentration, it is particularlyeasy to observe completion of the process of dissolution. It is,however, also possible to prepare the media by other conventional ways,e.g. using so called pre-mixtures, which can be e.g. homologous oreutectic mixtures of compounds or using so called multi-bottle-systems,the constituents of which are ready to use mixtures themselves.

The components B of the systems according to the present invention maybeneficially comprise one or more additives, like e.g.tri-alkoxy-substituted phenyl compounds, tetra-alkoxy-substituted phenylcompounds, penta-alkoxy-substituted phenyl compounds and compounds withbulky end groups.

By addition of suitable additives, the liquid crystal media according tothe instant invention can be modified in such a way, that they areusable in all known types of liquid crystal displays, either using theliquid crystal media as such, like TN-, TN-AMD, ECB-, VAN-AMD and inparticular in compo-site systems, like PDLD-, NCAP- and PN-LCDs andespecially in HPDLCs.

The melting point T(C,N), the transition from the smectic (S) to thenematic (N) phase T(S,N), the clearing point T (N,I), the transitiontemperature from the cholesteric phase to the blue phase (T(Ch,BP) alsocalled T(N*,BP)), the transition temperature from the blue phase to theisotropic phase (T(BP,I)) and all other transition temperatures of theliquid crystals are given in degrees centigrade.

In the compounds of the mesogenic host mixture, component B comprisesone or more compounds which have one or more linking groups (e.g. Z²¹and/or Z²² and/or Z²³ for the compounds of formula II) which is/aredifferent from a single bond. Preferably these linking groups areselected from —CO—O—, —O—CO—, —CF₂—O— and —O—CF₂—.

In a preferred embodiment of the present invention the polymer precursorcomprises reactive compounds, preferably of formula I, preferably itscomponent A comprises, preferably it consists of, compounds of formula Iwhich have one or more linking group or groups Z¹¹ to Z¹⁴, which aredifferent from a single bond, which are identical to the linking groupor linking groups, which are different from a single bond, which arepresent in the majority (either by mass % or, preferably, by mole %) ofthe compounds of the mesogenic host mixture.

In the present application and especially in the following examples, thestructures of the liquid crystal compounds are represented byabbreviations also called acronyms. The transformation of theabbreviations into the corresponding structures is straight forwardaccording to the following two tables A and B. All groups C_(n)H_(2n+1)and C_(m)H_(2m+1) are straight chain alkyl groups with n respectively mD-atoms. The interpretation of table B is self evident. Table A doesonly list the abbreviations for the cores of the structures. Theindividual compounds are denoted by the abbreviation of the corefollowed by a hyphen and a code specifying the substituents R¹, R², L¹and L² follows:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H HnOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) HH n C_(n)H_(2n+1) CN H H nN.F C_(n)H_(2n+1) CN H F nN.F.F C_(n)H_(2n+1)CN F F nF C_(n)H_(2n+1) F H H nF.F C_(n)H_(2n+1) F H F nF.F.FC_(n)H_(2n+1) F F F nOF OC_(n)H_(2n+1) F H H nCl C_(n)H_(2n+1) Cl H HnCl.F C_(n)H_(2n+1) Cl H F nCl.F.F C_(n)H_(2n+1) Cl F F nCF₃ CnH_(2n+1)CF₃ H H nOCF₃ C_(n)H_(2n+1) OCF₃ H H nOCF₃.F C_(n)H_(2n+1) OCF₃ H FnOCF₃.F.F C_(n)H_(2n+1) OCF₃ F F nOCF₂ C_(n)H_(2n+1) OCHF₂ H H nOCF₂.FC_(n)H_(2n+1) OCHF₂ H F nOCF₂.F.F C_(n)H_(2n+1) OCHF₂ F F nSC_(n)H_(2n+1) NCS H H nS.F C_(n)H_(2n+1) NCS H F nS.F.F C_(n)H_(2n+1)NCS F F rVsN C_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H rEsNC_(r)H_(2r+1)—O—C_(s)H_(2s)— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) HH nF.Cl C_(n)H_(2n+1) Cl H F

TABLE A

TABLE B

Particular preference is given to liquid-crystalline mixtures which,besides the compounds of the formula I, comprise at least one, two,three or four compounds from Table B.

TABLE C Table C shows possible dopants according to component D whichare generally added to the mixtures alone or in combination two, threeor more) according to the invention.

The liquid crystal media according to the instant invention do containpreferably

-   -   four or more compounds selected from the group of compounds of        tables A and B and/or    -   five or more compounds selected from the group of compounds of        table B and/or    -   two or more compounds selected from the group of compounds of        table A.

EXAMPLES

The examples given in the following are illustrating the presentinvention without limiting it in any way.

However, the physical data especially of the compositions both of thepolymer precursors and of the mesogenic host mixtures illustrate to theexpert which properties can be achieved in which ranges. The combinationof the various properties which can be preferably achieved is thus welldefined.

In the following set of examples (examples 1-1 to 1-6 and 2-1 to 2-7)the influence of monomers and of cross-linkers is investigated formixtures containing a combination of monoacrylated reactive mesogen(MRM) and diacrylated reactive mesogen (DRM).

Examples 1-1 to 1-7 and Comparative Example 1

In this first set of examples (examples 1-1 to 1-7) the influence of themono-reactive monomers is investigated.

A small amount of photoinitiator 2,2-dimethoxy-1,2-diphenyl-ethanone

(commercially known as Irgacure-651, here also short IRG-651) is addedto the mixture. A chiral dopant with a high value of the helicaltwisting power (HTP), R-5011, obtainable from Merck KGaA, is added tothe mixture in concentrations from 2.8% to 3.8%. The HTP of the chiraldopant R-5011 is measured as 130 μm⁻¹ in the polar host mixture A-0 withthe composition given in the table below,

TABLE 1 Composition and Properties of Host Mixture A-0 CompoundConcentration/ Abbreviation mass-% Physical Properties GZU-3A-N 15.0T(N, I) = 56.5° C. GZU-4A-N 15.0 GZU-4O-N 15.0 Δn (20° C., 589 nm) =0.164 UZU-3A-N 8.0 CUZU-2-N 9.0 CUZU-3-N 9.0 CUZU-4-N 9.0 HP-3N.F 6.0HP-4N.F 6.0 HP-5N.F 8.0 Σ 100.0

The types of cells used are typically either 10 μm thick cells withoutany alignment layers or 50 μm thick SSCT cells with planar alignment asthicker samples are occasionally required to allow for the opticalobservation of the Blue Phases. The cells have a size of approximately2.0 cm×2.5 cm. The electrode area is about 1.0 cm×1.0 cm. They arefilled by capillary action in an oven at a temperature of typically 100°C. Before polymerisation, the mixtures are characterised by polarisingmicroscopy and their transition temperatures are measured on heating at1° C./min. The experimental set-up consists of an Olympus BX51polarising microscope equipped with a Linkam temperature programmer andhot-stage.

Polymerisation experiments are carried out using an EFOS UV lamp at 1.5mW/cm² supplied with a broadband filter (320 nm to 500 nm). Initially,the sample is maintained at a temperature in the Blue Phase regime.After each increment of 15 s of UV irradiation, the texture of the cellis checked under polarising microscope to assess any changes. If a phasetransition has occurred, the temperature for the next step of UVirradiation is changed accordingly. Total exposure times are typically120 s at which stage, the final texture is stabilised.

As host mixture the mixture A-0 described above is used.

The compounds of formula IA are investigated in mixtures with thecomposition (in weight-%) given in the following table, table 5.

TABLE 2 Composition of the mixtures investigated in examples 1-1 to 1-6Compound/Mixture Concentration/ Abbreviation mass-% Respective comp. offormula IA 7.0 Comp. of formula IB-6 5.0 R-5011 2.8 Irgacure-651 0.6 A-084.6 Σ 100.0

The phase behaviour of the systems before and after polymerisation isgiven in the following table, table 3.

TABLE 3 Phase behaviour of examples 1-1o 1-6 and of comparative example1 Com- Expl. pound of Phases # formula Phases before curing BP aftercuring C.E. 1 none N* 47.1 BPI 47.6 BPII 51.4 I not applicable 1-1 IA-1N* 49.9 BPI 51.1 I −20° C. to 47° C. 1-2 IA-2 N* 30.9 BPI 32.5 BPIII^(§) −20° C. to 35° C. 1-3 IA-3 N* 30.3 BPI 31.7 BPIII 33.5 I −20° C. to40° C. 1-4 IA-4 N* 42.6 BP ^(§) −20° C. to 40° C. ^(§§) 1-5 IA-5 N* 47.8BPI 49.5 BPIII ^(§) −20° C. to 37° C. 1-6 IA-6 N* 47.3 BPI 48.5 BPII49.1 −20° C. to 46° C. BPIII 51.5 Iso 1-7 IA-7 n.d. −20° C. to 46.5° C.Remarks: n.d. not deternined, ^(§) no transition to isotropic phaseobserved and ^(§§) small areas of cholesteric (N*) present in the cellsbesides the Blue Phase (BP).

The best results obviously are obtained for examples 1-1, 1-6 and 1-7.

Examples 2-1 to 2-7

In this second set of examples (examples 2-1 to 2-7) the influence ofthe direactive monomers, the cross-linkers is investigated.

Here again the host mixture A-0 is used.

The compounds of formula IB are investigated in mixtures with thecomposition (in weight-%) given in the following table, table 4.

TABLE 4 Composition of the mixtures investigated in examples 2-1 to 2-7Compound/Mixture Concentration/ Abbreviation mass-% Comp. of formulaIA-1 7.0 Respective comp. of formula IB 5.0 R-5011 3.8 Irgacure-651 0.6A-0 84.6 Σ 100.0

The phase behaviour of the systems before and after polymerisation isinvestigated as described under example 1 and the results are given inthe following table, table 5.

TABLE 5 Phase behaviour of examples 2-1o 2-7 Com- Expl. pound of Phases# formula Phases before curing BP after curing 2-1 IB-1 N* 48.4 BPI 49.5BPIII 50.9 I −20° C. to +37° C. ^(§§) 2-2 IB-2 N* 41 BPI 41.5 BPIII 42 I−20° C. to +40° C. ^($) 2-3 IB-3 N* 48.3 BPI 49 Iso −20° C. to +42° C.2-4 IB-4 N* 40.5 BPI 41.8 BPIII 42.5 I −20° C. to +39° C. 2-5 IB-5 N*37.9 BPI 38.3 BPIII 38.4 I −20° C. to +38° C. ^(§§) 2-6 IB-6 N* 43 BPI45 I −20° C. to +36° C. 2-7 IB-7 N* 47 BPI 48 BPIII 50 I 32° C. to 44°C. Remarks: ^(§) dark BP, probably BPIII and ^(§§) small areas ofcholesteric (N*) present in the cells besides the Blue Phase (BP).

The best results obviously are obtained for examples 2-2, 2-3 and 2-6.

Comparative Example 2

A combination of a 2-ethylhexylacrylate (abbreviated as EHA), anon-mesogenic mono-reactive monomer and the compound of formula IB-6were added to highly polar host mixture A-0 in the concentration givenin the following table, table 6.

TABLE 6 Composition of the mixtures investigated in example 1Compound/Mixture Concentration/ Abbreviation mass-% EHA 2.5 Comp. offormula IB-6 5.0 R-5011 2.8 Irgacure-651 0.4 A-0 89.3 Σ 100.0

This precursor is investigated as described under example 1. Phaseseparation between the non-mesogenic monomer EHA and the LC host occursin the host mixture filled in the cell with a thickness of 10 μm andwithout alignment layer after 2 mins polymerisation by exposure to 1.5mW/cm² UV light leading to the darker domains under the microscope,being polymer-rich regions and to nucleation of dendritic chiral nematicdefects.

Examples 3.1 to 3.4 and Comparative Example 3

To host mixture A-0 the compound of formula IA-1, as mono-reactivemesogenic compound, and the compound of formula IB-6, as di-reactivemesogenic compound are added in various concentrations, together with2.8% of the chiral dopant R-5011 and a small concentration (typically0.6%) of the photo-intiator Irgacure-651 (short IRG-651). Thecompositions are given in the following table, table 7. The ratio of theconcentration of mono-reactive mesogenic compound to that of thedi-reactive mesogenic compound is kept constant at 1.4, whereas thetotal concentration of the reactive mesogens is varied in steps of 3%from 6% to 18%.

TABLE 7 Composition and results of examples 3.1 to 3.4 and ofcomparative example 3 Example No. C.E. 3 3.1 3.2 3.3a 3.3b 3.4Composition c(R-5011)/% 2.8 c(IRG-651)/% 0.6 1.06 0.6 c(IA-1)/% 3.5 5.257.0 8.75 10.5 c(IB-6)/% 2.5 3.75 5.0 6.25 7.5 c(IA-1) + c(IB-6)/% 6.09.0 12.0 15.0 18.0 Characteristic Temperatures T₂/° C. none 38.0 39.034.0 33.0 31.0 T₃/° C. none 38.0 30.0 25.0 25.0 25 T₁/° C. none 38.0−1.0 −3.5 −1.0 1.0 ΔT(BP)/° none 0.0 40.0 37.5 34 30.0 ΔT(FR)/° none 0.09.0 9.0 8.0 6.0 Characteristic Voltages T_(op.)/° C. none 38 10.0 10.010.0 10.0 V_(10, min)/V none 17 17.0 n.d. 20.0 31.0 V_(90, min)/V none34 36.0 n.d. 47.0 64.0 V_(100, min)/V none 38 41.0 52.0 55.0 74.0

The resulting mixtures are filled into test cells and cured byillumination with UV and investigated. In this example and in thefollowing examples test cells with an approximate size of 1.0 cm×1.0 cmare used. They have interdigital electrodes in a striped (comb-shaped)pattern on the inside of one substrate. The cells are filled on a hotplate having a temperature of about 80° C. to 100° C., while laying in ahorizontal position. The characteristic temperatures and the minimumvalues of the characteristic voltages are determined. The results arealso summarised in the preceeding table, table 8.

Obviously the total concentration of the polymer precursor of 6% used incomparative example 3 is too small to stabilise a blue phase, whereasthat of 9% used in the example 3.1 is just sufficient for this purposeunder the applied conditions.

The temperature dependence of the characteristic voltages of the cell ofexample 3.2 is given in table 8, below.

TABLE 8 Temperature dependence of characteristic voltages of example 3.2T/° C. V₁₀/V V₉₀/V −10.0 34.0 78.0 −5.1 22.0 48.0 −0.3 18.0 38.0 4.917.0 36.0 9.6 17.0 36.0 15.0 17.0 37.0 20.0 19.0 39.0 25.0 21.0 41.030.1 22.0 44.0 34.9 25.0 47.0 39.8 28.0 54.0 40.1 29.0 55.0 45.1 44.082.0 50.1 61.0 116.0

The temperature range, over which the response times τ_(on) and.τ_(off), both are below 5 ms and at the same time the characterisicvoltage are still sufficiently low, for this example (3.2) extends from30.1° C. to 40.1° C.

Example 4

Similar to example 3, 12% of the reactive mesogens and 0.6% of thephotoinitiator Irgacure-651 are added together with the chiral dopantR-5011 to host mixture A-0. Now, however 4.0%, of R-5011 are used, assummarised in the following table, table 10. The resulting mixture isfilled into test a cell and cured by illumination with UV andinvestigated. The characteristic temperatures and the minimum values ofthe characteristic voltages are determined. The results are alsosummarised in the following table, table 9. The data for examples 3.2 to3.4 are included in this table for comparison.

TABLE 9 Composition and results of examples 4 and 5 Example No. 3.2 3.3a3.4 4 5 Composition c(IRG-651)/% 0.6 c(R-5011)/% 2.8 4.0 2.7 c(IA-1)/%7.0 8.75 10.5 7.0 6.8 c(IB-6)/% 5.0 6.25 7.5 5.0 4.85 [c(IA-1) + 12.015.0 18.0 12.0 11.65 c(IB-6))/% c(TRI)/% none 3.0 CharacteristicTemperatures T₂/° C. 39.0 34.0 31.0 30.0 29.0 T₃/° C. 30.0 25.0 25 30.025.0 T₁/° C. −1.0 −3.5 1.0 0.0 0.0 ΔT(BP)/° 40.0 37.5 30.0 30.0 29.0ΔT(FR)/° 9.0 9.0 6.0 0.0 4.0 Characteristic Voltages T_(op.)/° C. 10.010.0 10.0 5.0 5.0 V_(100, min)/V 41.0 52.0 74.0 57.0 40.0

Example 5

Again similar to example 3, totally 11.65% of the reactive mesogens and0.6% of the phitoinitiator Irgacure-651 are added together with 2.7% ofthe chiral dopant R-5011 to host mixture A-0. Now, however, additionally3.0% of the trialkoxy-compound (short TRI) of the formula

are added to the host mixture A-0, as summarised in the preceedingtable, table 10. The resulting mixture is filled into a test cell andcured by illumination with UV and investigated. The characteristictemperatures and the minimum values of the characteristic voltages aredetermined. The results are also summarised in the preceeding table,table 10.

Examples 6.1 to 6.4

In these examples, besides 12% of the reactive mesogens, 0.6% of thephitoinitiator Irgacure-651 and 2.8% of the chiral dopant R-5011 to hostmixture A-0, used in example 3, various amounts of compounds of the typeAUUQU-n-F are added, as summarised in the following table, table 10. Theresulting mixtures are filled into test cells and cured by illuminationwith UV and investigated. The characteristic temperatures and theminimum values of the characteristic voltages are determined. Theresults are also summarised in the following table, table 11. The datafor example 3.2 are included in this table for comparison.

TABLE 10 Composition and results of examples 6.1 to 6.4 Example No. 3.26.1 6.2 6.3 6.4 Composition c(IRG-651)/% 0.6 c(R-5011)/% 2.8 c(IA-1)/%7.0 c(IB-6)/% 5.0 c(IA-1) + c(IB-6)/% 12.0 c(AUUQU-1-F)/% none none none8.0 9.0 c(AUUQU-2-F)/% 10.0 c(AUUQU-3-F)/% 15.0 10.0 11.0 c(AUUQU-4-F)/%none 10.0 7.0 9.0 c(AUUQU-5-F)/% none 5.0 7.0 c(AUUQU-6-F)/% none 7.0c(AUUQU-7-F)/% 7.0 Σc(AUUQU-n-F)/% 0.0 15.0 30.0 40.0  60.0Characteristic Temperatures T₂/° C. 39.0 45.0 45.0 n.d. n.d. T₃/° C.30.0 25.0 25.0 n.d. n.d. T₁/° C. −1.0 0.0 <15.0 n.d. n.d. ΔT(BP)/° 40.045.0 >30.0 n.d. n.d. ΔT(FR)/° 9.0 20.0 20.0 n.d. n.d. CharacteristicVoltages T_(op.)/° C. 10.0 6.0 15.0 n.d. n.d. V_(100, min)/V 41.0 36.035.0 n.d. n.d. Remarks: n.d.: not determined.

Examples 7 and 8

In these examples, like in examples 6.1 to 6.4, additional mesogeniccompounds are added to the host mixture A-0, besides the polymerprecursor, the chiral dopant and the photo-initiator. Now, however, thecompounds added are terminally CN-substituted. The compound used inexample 7 is AUZU-3-N and the compound used in example 8 is AUUQU-3-N.The concentration used is 15% in each case, as shown in the followingtable, table 12. The results are also shown in the following table,table 11.

TABLE 11 Composition and results of examples 7 and 8 Example No. 3.2 6.17 8 Composition c(IRG-651)/% 0.6 c(R-5011)/% 2.8 c(IA-1)/% 7.0 c(IB-6)/%5.0 c(IA-1) + c(IB-6)/% 12.0 Compound none AUUQU-3-F AUZU-3-N AUUQU-3-Nc(Compound)/% 0.0 15.0 Characteristic Temperatures T₂/° C. 39.0 45.045.0 55.0 T₃/° C. 30.0 25.0 35.0 35.0 T₁/° C. −1.0 0.0 0.0 5.0 ΔT(BP)/°40.0 45.0 45.0 50.0 ΔT(FR)/° 9.0 20.0 20.0 20.0 Characteristic VoltagesT_(op.)/° C. 10.0 6.0 10.0 10.0 V_(100, min)/V 41.0 36.0 39.0 32.0Remarks: n.d.: not determined.

The temperature dependence of the characteristic voltages of the cell ofexample 8 is given in table 12 below.

TABLE 12 Temperature dependence of characteristic voltages of example 8T/° C. V₁₀/V V₉₀/V −10.0 56 126.0 −5.0 28 60.0 0.0 18 38.0 10.0 14.028.0 20.1 15.0 29.0 29.9 16.0 31.0 30.2 16.0 31.0 35.2 17.0 32.0 40.018.0 33.0 45.0 18.0 35.0 50.0 20.0 38.0 55.0 21.0 44.0 60.0 37.0 70.0

The temperature range over which the response times τ_(on) and .τ_(off),both are below 5 ms and at the same time the characteristic voltage arestill sufficiently low for this example (3.2) extends from 35.2° C. to55.0° C.

Examples 9.1 to 9.3 and Comparative Examples 9.1 and 9.2

In comparative example 9.1 the total amount of 7% by weight of themono-reactive mesogenic compound IA-1 used in example 3.2 is replaced byan equal percentage (7% by weight) of the non-mesogenic mono-reactivecompound EHA used in comparative example 2. Otherwise the composition iskept unchanged. The resulting system does not show a stabilisedBP-texture under the microscope.

In comparative example 9.24% by weight of the non-mesogenicmono-reactive compound EHA used in comparative example 2 is usedtogether with 8% of the di-reactive mesogenic compound IB-6. The resultsobtained are shown in the following table, table 13.

In examples 9.1 to 9.3 the mono-reactive mesogenic compound IA-1 is usedsimultaneously with the non-mesogenic mono-reactive compound EHA. Theconcentration of the polymer precursors is kept constant at 12%, whereasthe relative concentrations of the mono-reactive compounds are changedsystematically, as shown in the following table, table 13.

TABLE 13 Composition and results of examples 9.1 to 9.4 and comparativeexample 9.2 Example No. 3.2 9.1 9.2 9.3 9.4 C.E. 9.2 Compositionc(IRG-651)/% 0.6 0.61 0.62 0.64 c(R-5011)/% 2.8 2.84 2.86 2.90 2.92 3.0c(IA-1)/% 7.0 5.6 4.9 3.5 2.8 0.0 c(EHA)% 0.0 0.8 1.2 2.0 2.4 4.0c(IB-6)/% 5.0 5.6 5.0 6.5 6.8 8.0 [c(IA-1) + c(EHA) + 12.0 c(IB-6)]/%Characteristic Temperatures T₂/° C. 39.0 n.d. n.d. n.d. 36.0 55.0 T₃/°C. 30.0 n.d. n.d. n.d. 24.0 35.0 T₁/° C. −1.0 n.d. n.d. n.d. −5.0 0.0ΔT(BP)/° 40.0 n.d. n.d. n.d. 41.0 55.0 ΔT(FR)/° 9.0 n.d. n.d. n.d. 12.030.0 Characteristic Voltages T_(op.)/° C. 10.0 n.d. n.d. n.d. 0.0 5.0V_(100, min)/V 41.0 n.d. n.d. n.d. 44.0 54.0 Remarks: n.d.: notdetermined.

For the systems of examples 3.2 and 9.1 to 9.3, as well as forcomparative examples 09.1 and 9.2 the characterisic temperature(s)is/are monitored during the polymerisation process at appropriateregular time intervals until no further change is observed.

The results are compiled in the following table, table 14.

TABLE 14 Composition and charactristic temperatures duringpolymerisation of examples 9.1 to 9.3 and comparative example 9.2Example No. 3-2 9-1 9-2 9-3 9.4 C.E. 9-2 C.E. 9-1 c(IRG-651)/% 0.6 0.610.62 0.64 0.6 c(R-5011)/% 2.8 2.84 2.90 2.90 2.92 3.0 2.8 c(IA-1)/% 7.05.6 3.5 3.5 2.8 0.0 c(EHA)% 0.0 0.8 2.0 2.0 2.4 4.0 7.0 c(IB-6)/% 5.05.6 6.5 6.5 6.8 8.0 5.0 [c(IA-1) + 12.0 c(EHA) + c(IB-6)]/%Characteristic Temperatures During Curing Time(curing)/S T₂/° C.  0 48.343.5 39.9 35.8 31.0 17.0 0.0  5 n.d. n.d. n.d. n.d. 31.0 17.0 0.0  10n.d. 42.8 39.9 35.8 31.0 18.0 −3.0  15 46.2 n.d. n.d. n.d. 31.0 19.0−3.0  20 n.d. 41.0 38.6 34.9 31.0 20.0 n.d.  25 n.d. n.d. n.d. 34.9 31.021.0 n.d.  30 43.6 39.2 37.4 n.d. 31.0 22.0 10.0  40 n.d. 39.2 n.d. 34.331.0 23.0 n.d.  45 42.0 n.d. n.d. n.d. 31.0 n.d. n.d.  50 n.d. n.d. n.d.n.d. n.d. 24.0 n.d.  60 41.2 39.2 n.d. 34.3 n.d. 25.0 20.0  75 n.d. n.d.n.d. n.d. 31.0 26.0 n.d.  90 40.0 39.2 37.4 n.d. n.d. 27.0 24.2 105 n.d.n.d. n.d. n.d. n.d. 28.0 n.d. 120 40.0 39.2 n.d. n.d. 31.0 29.0 27.8 135n.d. n.d. 37.4 34.3 n.d. n.d. n.d. 140 n.d. n.d. n.d. n.d. n.d. 29.5n.d. 150 n.d. 39.2 n.d. n.d. n.d. n.d. 30.2 160 n.d. n.d. n.d. n.d. n.d.30.0 n.d. 180 40.0 39.2 37.4 34.3 31.0 31.0 32.2 210 n.d. 39.2 n.d. n.d.n.d. 31.5 n.d. 240 n.d. 39.2 n.d. n.d. n.d. 32.0 34.9 300 n.d. n.d. n.d.n.d. n.d. 32.0 36.5 360 n.d. n.d. n.d. n.d. n.d. 32.0 37.7 420 n.d. n.d.n.d. n.d. n.d. n.d. 38.6 540 n.d. n.d. n.d. n.d. n.d. n.d. 40.0 Remarks:n.d.: not determined.

As can be seen from the results in table 14 appropriate selection bothof mono-reactive compounds being mesogenic and of mono-reactivecompounds being non-mesogenic, as well as selecting their appropriatemixing ratio in the polymer precursor allows to minimise the change ofthe transition temperature during the process of polymerisation, inorder to keep the system in the preferred phase, preferably the BluePhase, and thus makes a control and adjustment of the temperature duringthe process of polymerisation obsolete.

Especially the results for example 9.2, which are almost completelycompensated for temperature change during the process, and for example9.3 clearly illustrate this effect.

In particular, example 9.4 shows almost no temperature change of T₂after polymerisation. Thus, example 9.4a, with stepwise polymerisatoin,as described above, is repeated, but with 180 mS exposure to UV in onesingle application as additional example 9.4b. The result of theprevious example (9.4a) is well repruduced also this way.

In contrast example 3.2 shows a marked decrease of the transitiontemperature during polymerisartion, whereas comparative examples 9.1 and9.2 both show the opposite change of the transition temperature uponpolymerisation, both of which are undesired.

1. Mesogenic system comprising a) a polymeric component, component A,obtained or obtainable from polymerisation of a precursor comprising oneor more mesogenic mono-reactive compounds, one or more di-reactivecompounds, which optionally are also mesogenic compounds and optionallya photo-initiator and b) a low molecular weight component, component B,comprising one or more mesogenic compounds and one or more chiraldopants, exhibiting a Blue Phase.
 2. System according to claim 1,characterized in that, component A comprises one or more mesogenicdi-reactive compounds.
 3. System according to claim 1, characterised inthat, the precursor of component A comprises one or more non-mesogenic(isotropic) mono-reactive compounds.
 4. System according to claim 1,characterized in that the precursor of component A comprises one or morecompounds, which on their own lead or would lead to an increase of thecharacteristic temperatures (e.g. the transition temperature from theBlue Phase into the isotropic phase) during and/or upon itspolymerisation and one or more compounds which on their own lead orwould lead to a decrease of the characteristic temperatures (e.g. thetransition temperature from the Blue Phase into the isotropic phase)during and/or upon its polymerisation.
 5. System according to claim 1,characterized in that its characteristic temperatures do not changesignificantly during and/or upon polymerisation of the precursor of thepolymer.
 6. System according to claim 1, characterized in that, it has aBlue Phase extending at least over a temperature range from −10° C. orbelow to +50° C. or above.
 7. Light modulation element, characterized inthat, it comprises a system according to claim
 1. 8. Use of a systemaccording to claim 1 as a light modulation medium.
 9. Use of a systemaccording to claim 1 in a light modulation element.
 10. Electro-opticaldisplay, characterized in that it comprises a system according to claim1.